Active motion control of a hydraulic free piston engine

The free piston engine (FPE), as an alternative of the conventional internal combustion engine, could significantly impact the energy consumption and emissions of both on-highway and off-highway vehicles. In an FPE, the piston motion is dependent on the combustion chamber gas dynamics and the loading dynamics in real time. One of the technical barriers that prevents the wide spread of this technology is the lack of precise piston motion control. In this paper, we present the modeling and control of a hydraulic FPE with an opposed-piston opposed-cylinder design. Specifically, a comprehensive system model is first built and validated to study the dynamics of the engine operation. The simulation studies lead to the design of an active piston motion controller, which acts as a virtual crankshaft by utilizing energy in the storage element to regulate the piston to follow a predefined trajectory. With a designated optimal trajectory, the virtual crankshaft ensures stable and robust operation in engine motoring. Preliminary combustion testing results and analysis are also included in this paper.